A. Field of the Invention
The present invention relates to coated particulate matter wherein the particles are individually coated with a first set of one or more layers of a curable resin, for example, a combination of phenolic/furan resin or furan resin or phenolic-furan-formaldehyde terpolymer, on a proppant such as sand, and the first set of layers is coated with a second set of one or more layers of a curable resin, for example, a novolac resin. Methods for making and using this coated product as a proppant, gravel pack and for sand control are also disclosed.
B. Background Description
The term “proppant” is indicative of particulate material which is injected into fractures in subterranean formations surrounding oil wells, gas wells, water wells, and other similar bore holes to provide support to hold (prop) these fractures open and allow gas or liquid to flow through the fracture to the bore hole.
U.S. Pat. No. 4,694,905 to Armbruster, incorporated herein by reference, discloses coated particulate matter wherein the particles are individually coated with a cured combination of phenolic/furan resin or furan terpolymer resin to form a precured resin coating on a proppant such as sand, thereby substantially improving the chemical resistance of the proppant over one having a straight phenolic precured coating. Another embodiment of this invention involves the use of multiple resin coatings on the particulate matter to form a final layered coating containing the desired amount of cured resin.
U.S. Pat. No. 4,722,991 to Armbruster, incorporated herein by reference, discloses a terpolymer is prepared from phenol, furfuryl alcohol and formaldehyde wherein a substantial amount of the furfuryl alcohol is catalytically reacted by means of a water soluble multivalent metal salt catalyst, and wherein the reaction is carried out under essentially hydrous conditions.
U.S. Pat. No. 4,677,187 to Armbruster, incorporated herein by reference, discloses a furfuryl alcohol formaldehyde resin that can be prepared using a water soluble multivalent metal salt catalyst.
U.S. Pat. No. 4,888,240 to Graham et al., incorporated herein by reference, discloses a resin coated proppant particle that comprises a particulate substrate, a cured inner resin coating and a curable outer resin coating.
U.S. Pat. No. 5,837,656 to Sinclair et al., incorporated herein by reference, discloses a resin coated proppant particle that comprises a particulate substrate, an inner coating of a curable resin and an outer coating of a cured resin. These resin coated particles are produced by first coating the substrate with a reactive resin. A second or outer coating of a resin is then coated over the inner curable resin coating and subjected to conditions of time and temperature sufficient to cure the outer coating while the inner coating remains curable.
Proppants are commonly used to prop open fractures formed in subterranean formations such as oil and natural gas wells during hydraulic fracturing. The proppants may be precured or curable. The precured proppants are cured prior to insertion into the subterranean formation. The curable proppants are cured downhole to form a consolidated proppant pack. Resin formulations typically used for curable coatings on proppant substrates (sand, ceramic, etc.) result in a highly crosslinked coating on the surface of the substrates. Although this usually results in maximizing the thermal properties of the coatings, it is not necessarily a preferred condition for coatings of interest to the oilfield industry where temperatures rarely ever exceed 400° F., but are subjected to stresses that will breakdown brittle bonding.
Curable phenolic resin coated sands have been commercially available for use as propping agents. A curable phenolic resin coating has a phenolic resin which is at least partially, and not fully cured, in contrast with the term “precured” which means that the phenolic resin coating is a cured coating, which is also commercially available.
Another aspect of obtaining production from a subterranean formation is that to extract hydrocarbons such as natural gas and crude oil from the earth's subsurface formations, boreholes are drilled into hydrocarbon bearing production zones. However, production of oil, gas and water from unconsolidated or weakly consolidated formations is normally accompanied by the production of formation sand particles along with the produced fluids. The production of sand with the well fluids poses serious problems such as the erosion of sub-surface and surface production facilities and the accumulation of the sand in the wellbore and surface separators. Several methods such as gravel packing, screens and plastic consolidation have been in use for many years with varying success. However, these methods have several-technical and cost limitations. Further discussion of sand control is presented by U.S. Pat. No. 6,364,019 incorporated herein by reference in its entirety.
To maintain the productivity of a borehole and control the flow of hydrocarbon fluids from the borehole, numerous prior art devices and systems have been employed to prevent the natural forces from collapsing the borehole and obstructing or terminating fluid flow therefrom. One such prior art system provides a full depth casement of the wellbore whereby the wellbore wall is lined with a steel casing pipe that is secured to the bore wall by an annulus of concrete between the outside surface of the casing pipe and the wellbore wall. The steel casing pipe and surrounding concrete annulus is thereafter perforated by ballistic or pyrotechnic devices along the production zone to allow the desired hydrocarbon fluids to flow from the producing formation into the casing pipe interior. Usually, the casing interior is sealed above and below the producing zone whereby a smaller diameter production pipe penetrates the upper seal to provide the hydrocarbon fluids a smooth and clean flowing conduit to the surface.
Another well completion system protects the well borewall production integrity by a tightly packed deposit of aggregate comprising sand, gravel or both between the raw borewall and the production pipe thereby avoiding the time and expense of setting a steel casing from the surface to the production zone which may be many thousands of feet below the surface. The gravel packing is inherently permeable to the desired hydrocarbon fluid and provides structural reinforcement to the bore wall against an interior collapse or flow degradation. Such well completion systems are called “open hole” completions. The apparatus and process by which a packed deposit of gravel is placed between the borehole wall and the production pipe is encompassed within the definition of an “open hole gravel pack system.” Unfortunately, prior art open hole gravel pack systems for placing and packing gravel along a hydrocarbon production zone have been attended by a considerable risk of precipitating a borehole wall collapse due to fluctuations in the borehole pressure along the production zone. These pressure fluctuations are generated by surface manipulations of the downhole tools that are in direct fluid circulation within the well and completion string. Further discussion of gravel packs is presented by U.S. Pat. No. 6,382,319 incorporated herein by reference.
It would be desirable to provide improved particles for use as proppants, gravel pack, and/or for sand control in subterranean formations.